1. Field of the Invention
This invention relates to an internal combustion engine having an oil chamber.
2. Description of Background Art
An internal combustion engine for a vehicle is known which includes a transmission case provided on one side of a crankcase for supporting a crankshaft and further includes a cover member provided on the transmission case for covering the sides while a transmission is accommodated by the transmission case and the cover member.
In an engine of the type described, an oil chamber is formed at a lower portion of the crankcase and oil in the oil chamber is pressure-fed to a cylinder or the like of the engine by an oil pump provided between the crankcase and the transmission case. See, for example, Japanese Patent Laid-Open No. 2007-170314.
However, according to the conventional structure, since oil fed into the cylinder or the like is heated and is pressure-fed to the cylinder or the like by the oil pump immediately after it returns into the oil chamber, although the oil radiates some heat through an outer surface of the crankcase only for a short period of time for which the oil stays in the oil chamber after returned, the amount of the radiated heat is small. Therefore, the oil is reserved normally in a state wherein the temperature thereof remains high.
In an air-cooled engine, although the engine itself is cooled by heat radiating fins provided on the cylinder, unless an oil cooler is provided separately, the oil is cooled very little. Accordingly, in a conventional engine which does not include an oil cooler, if the engine is operating, then the oil basically continues to be heated.
On the other hand, although it is a possible idea to add a large-sized oil cooler to achieve compulsory cooling of the oil, this increases the number of parts and gives rise to an increase in the cost and the weight. In addition, since it is necessary to assure also the arrangement space for the parts, where the arrangement space cannot be assured, the addition of the oil cooler is difficult.